Física Médica UAEM ININ

📢 Career Opportunity in Medical Physics

Looking for a PhD opportunity in PET/CT imaging?

The University Medical Center Groningen (UMCG), Netherlands, is recruiting a PhD Candidate in PET/CT for Infection and Inflammation within the Marie Skłodowska-Curie Doctoral Network PREFERENCE. The project focuses on advancing PET/CT imaging for the detection of early-stage infection and inflammation.

🏥 Institution: University Medical Center Groningen (UMCG)

📍 Location: Groningen, The Netherlands

📅 Application deadline: 31 August 2026

🔗 Read more and apply:
https://www.efomp.org/index.php?r=jobs

Research EFOMP

📣 Estimada comunidad, nuevamente México será sede de los exámenes internacionales de certificación en Física Médica.

ℹ️ Mayor información aquí:

https://www.impcbdb.org/exam-session-in-mexico

¡Feliz inicio de semestre Comunidad Universitaria!
Cada semana es una nueva oportunidad para aprender, crecer y seguir construyendo nuestros sueños.
En la creemos en una comunidad cercana, incluyente y comprometida con el progreso de todas y todos.

✨ Que este inicio de semestre sea el comienzo de grandes logros.

💼 ¡Nuevas vacantes en el OIEA disponibles!

⏰ Revisa las que vencen pronto y no te quedes fuera.

Aplica ahora👇

Las 4 (5?) Rs de la y la importancia del de dosis en

The 5 Rs of Radiobiology
Why Fractionation Works in Radiation Therapy
Radiation therapy is not simply about delivering a high dose of radiation.

If that were true, we could treat every cancer in a single fraction.

Instead, most treatments are delivered over multiple sessions—a concept known as fractionation.

But why?

The answer lies in one of the most important principles in radiation oncology:

The 5 Rs of Radiobiology

These biological processes explain how normal tissues recover, how tumors respond, and why fractionated radiotherapy is so effective.

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1. Repair 🔧

What is Repair?

After radiation exposure, DNA damage occurs in both tumor cells and normal cells.

Healthy tissues have a remarkable ability to repair sublethal DNA damage between treatment fractions.

Tumor cells also attempt repair, but this process is often defective due to abnormalities in their DNA repair mechanisms.

Clinical Importance

- Protects normal tissues.
- Reduces late radiation toxicity.
- Allows higher total doses to be delivered safely.
- Forms the biological basis of daily fractionation.

Key Point:

«Normal tissues repair DNA damage more efficiently than most cancer cells.»

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2. Reoxygenation 🫁

Why Does Oxygen Matter?

Radiation kills cells primarily by generating free radicals that damage DNA.

Oxygen stabilizes this DNA damage, making it permanent.

Well-oxygenated tumor cells are 2–3 times more radiosensitive than hypoxic cells.

What Happens Between Fractions?

After radiation destroys oxygen-rich tumor cells:

- Blood flow improves.
- Previously hypoxic regions receive more oxygen.
- Remaining tumor cells become more radiosensitive before the next fraction.

Clinical Importance

This is one of the major reasons why fractionated radiotherapy is more effective than a single large dose.

Key Point:

«Better oxygenation = Better radiation response.»

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3. Redistribution (Reassortment) 🔄

The Cell Cycle Matters

Cells are not equally sensitive to radiation throughout the cell cycle.

Most Radiosensitive Phases

- G₂ Phase
- M Phase (Mitosis)

Most Radioresistant Phase

- S Phase

After each fraction:

Surviving tumor cells continue progressing through the cell cycle.

Many resistant cells eventually enter the highly radiosensitive G₂/M phases, making subsequent fractions more effective.

Clinical Importance

Fractionation increases the probability of irradiating tumor cells during their most vulnerable phase.

Key Point:

«Radiation becomes more effective when tumor cells enter G₂ and M phases.»

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4. Repopulation 📈

What is Repopulation?

Both normal tissues and tumor cells can divide and replace damaged cells during treatment.

This process is known as repopulation.

The Good Side

Healthy tissues regenerate and recover from radiation injury.

The Bad Side

Tumor cells may also proliferate, especially during prolonged treatment courses.

Accelerated repopulation is particularly important in:

- Head & Neck Cancer
- Cervical Cancer
- Lung Cancer

Clinical Importance

Unnecessary treatment interruptions can reduce tumor control.

Maintaining the prescribed treatment schedule is essential.

Key Point:

«Every unnecessary delay gives surviving tumor cells an opportunity to multiply.»

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5. Radiosensitivity 🎯

What is Radiosensitivity?

Different tissues and tumors respond differently to radiation.

Some tumors are destroyed with relatively low doses.

Others require much higher doses.

Highly Radiosensitive Tumors

- Lymphoma
- Seminoma
- Leukemia
- Pediatric tumors

Moderately Radiosensitive Tumors

- Breast cancer
- Prostate cancer
- Head & Neck cancer

More Radioresistant Tumors

- Melanoma
- Renal Cell Carcinoma
- Sarcoma
- Glioblastoma

Factors Affecting Radiosensitivity

- DNA repair capacity.
- Oxygenation.
- Cell cycle phase.
- Tumor genetics.
- Cellular differentiation.

Key Point:

«Not all cancers respond equally to the same radiation dose.»

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Why Are the 5 Rs Important?

Together, the 5 Rs explain why fractionated radiotherapy provides a therapeutic advantage:

✅ Protects normal tissues through Repair.

✅ Improves tumor oxygenation via Reoxygenation.

✅ Targets cells in sensitive phases through Redistribution.

✅ Highlights the importance of avoiding treatment interruptions because of Repopulation.

✅ Helps tailor treatment according to Radiosensitivity.

These principles form the biological foundation of modern radiation therapy.

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Summary Table

R| Main Benefit
🔧 Repair| Normal tissue recovery between fractions
🫁 Reoxygenation| Increases tumor radiosensitivity
🔄 Redistribution| Moves tumor cells into more radiosensitive phases
📈 Repopulation| Tissue regeneration—but also potential tumor regrowth
🎯 Radiosensitivity| Determines how different tumors respond to radiation

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Conclusion

The success of radiation therapy is determined not only by physics, but also by biology.

The 5 Rs of Radiobiology explain why fractionation works, why treatment schedules matter, and why every fraction contributes to improved tumor control while protecting healthy tissues.

Understanding these five biological principles is essential for every Radiation Therapist, Medical Physicist, Dosimetrist, and Radiation Oncologist.

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References

- Hall EJ, Giaccia AJ. Radiobiology for the Radiologist
- Joiner & van der Kogel. Basic Clinical Radiobiology
- IAEA Handbook of Radiation Oncology Physics
- ASTRO Educational Resources
- ESTRO School

Máscaras termoformables para

Porque también el Mundial de Futbol lleva vigilancia radiológica ☢️ Con la participación de Físicos Médicos UAEMéx.

Partículas minúsculas, pero con un gran impacto.

Los aceleradores de partículas aceleran electrones, protones e iones para propiciar avances significativos en los ámbitos de la atención oncológica, la energía limpia, la monitorización ambiental, la inocuidad de los alimentos, la industria e incluso el patrimonio cultural. Desde linac en hospitales hasta enormes sincrotrones, los aceleradores impulsan el avance científico mucho más allá de los laboratorios.